1. Field of the Invention
The present invention relates to an image reading apparatus, further in details, relates to an image reading apparatus aligning a plurality of pieces of line sensors, which are aligned with reading pixels in a row-like shape, in a zigzag shape in a main scanning direction and successively reading a large-sized draft formed with the image to be read and carried in a sub scanning direction orthogonal thereto by the line sensor.
2. Description of the Related Art
FIG. 11 is a view showing a constitution of a draft carrying type scanner which is an image reading apparatus of this kind, in the drawing, numeral 1 designates a scanner main body, numeral 2 designates a close contact type image sensor aligned with a plurality of pieces of reading elements including photoelectric conversing elements in a row-like shape successively such as 0, 1, 2, . . . , N−1, N in a main scanning direction of the drawing, numeral 3 designates a draft carrying portion, numeral 4 designates a draft pressing portion, numeral 5 designates a draft and numeral 7 designates a control portion.
A base 11 constituting a frame of the scanning main body is formed by having a channel-like shape in a sectional view thereof extended in the main scanning direction, and the base 11 is arranged with a plurality of close contact type image sensors S1, S2, S3, . . . in two rows in a zigzag shape to be remote from each other by an interval 1 in the sub scanning direction for reading a large-sized draft image of A0, A1. Further, contact glass 12 including a transparent glass member is provided on the base 11. An image reading portion includes the base 11, the close contact sensor 2, and the contact glass 12.
Front and rear portions in the sub scanning direction of the image reading portion are provided with the draft carrying portions 3 each constituted by a drive roller 31 transmitted with a rotation drive force by a rotation drive mechanism, not illustrated, and a pinch roller 32 which is a driven roller brought into press contact with the drive roller 31 to pinch the draft 5.
When a draft image is read by the image reading apparatus, first, the draft 5 is inserted to between the drive roller 31 and the pinch roller 32 provided on an upstream side in the sub scanning direction to be pinched thereby, and the drive roller is driven to rotate in an arrow mark direction of the drawing to carry the draft in the sub scanning direction. In synchronism with carrying the draft 5, the draft image is successively read by the sensor 2, the draft image is stored to be held by a line buffer 72 as data of each line in the main scanning direction, and image data of a total of the draft 5 is constituted to be formed by shifting from the data of each line read from the line buffer 72 by an amount of a distance (1) for separating the respective sensors in the sub scanning direction to synthesize by a frame memory 73.
The formed image data of the draft 5 is transmitted to a higher apparatus of a computer or the like via an interface circuit 74.
The close contact type image sensor 2 used in the image reading apparatus is provided such that a light ray irradiated from a light source 21 is reflected by the draft 5 to be incident on a lens array 22 to be focused on a line sensor 23 and therefore, in order to excellently read the image, it is indispensable that the draft 5 is carried by being brought into close contact with the contact glass 12. Hence, the image reading apparatus of the draft carrying type of this kind is constituted to be provided with the draft pressing portion 4 for pressing the draft 5 carried above the image reading portion to the contact glass to thereby urge the draft 5 in a direction of the contact glass 12 to be brought into close contact therewith.
According to the draft pressing mechanism, in order to bring the draft 5 into close contact with the contact glass 12, a pressing member 40 including a plate-like member having a plane the same as that of the contact glass is fixed in the main scanning and the sub scanning directions and the pressing member 40 is operated to the draft 5 from immediately thereabove and a pressing force includes a self weight thereof. (See, e.g. JP-A-2003-125159.)
According to the image reading apparatus for reading an image of a large-sized draft by aligning a plurality of line sensors in the zigzag shape, as described above, the apparatus is constituted to be provided with the drive rollers 31 and the pinch rollers which are the driven rollers brought into press contact with the draft 5 to be pinched thereby at the front and rear portions in the sub scanning direction of the image reading portion and provided with the draft pressing member 4 for bringing the draft 5 carried on the image reading portion into press contact with the contact glass 12 and therefore, there is brought about a drawback that a space of providing the draft carrying mechanism is needed in the sub scanning direction of the apparatus, thereby, it is difficult to downsize the apparatus, and by increasing a number of parts, fabricating cost is increased and the apparatus becomes expensive.
The invention is carried out to resolve the drawbacks.